(1) Field of the Invention
The present invention relates generally to acoustic projectors, and more particularly to a system and method for operating acoustic projectors over a wide bandwidth while reducing the power supplied and dissipated.
(2) Description of the Prior Art
Acoustic projectors of the type having multiple ceramic elements are used to provide wide bandwidth operation. Such projectors are normally powered by an amplifier tuned to the center of the frequency band of operation. For example, U.S. Pat. No. 4,652,786 to Mishiro recites a torsional vibration apparatus having a plurality of electrodes formed on the two surfaces of a circular member of electrostrictive material. Adjacent electrodes are simultaneously polarized so as to be mutually reversed in a circumferential direction. The electrodes essentially form multiple elements from the circular member. A high frequency voltage is tuned to the slide resonance frequency and impressed on the apparatus to induce resonant vibration. The electrodes are connected to a power supply through a transformer having the primary coil connected to the power supply, the midpoint of the secondary coil connected to ground and the ends of the secondary coil connected to the segmented electrodes in an alternating manner such that adjacent electrodes have opposite polarity. In a stack configuration, the ends of the secondary coil would be connected at each end of the stack. The power amplifier load at the frequency band edges is highly reactive with a large phase angle. This results in the power amplifier and its power source supplying substantial amounts of reactive power to the projector, with power being dissipated in the amplifier. A need exists to operate acoustic projectors more efficiently over a wide bandwidth.